low compression after rebuild- noise - bent valve?

[KA1J]

I replaced the rings and cams, honed the cylinders and put a new base gasket, head gasket YICS O-rings and replaced the valve seals.

Yesterday I got the cams in place and then set up the chain to the sprockets. At first the chain did not move the cams. I didn't run the crank in a full revolution, only the 45 degrees it said in the manual to move the pointer to "C" and when the cams didn't follow I got help and discovered the chain was not on the sprocket.

Got it on and after turning the crank till the dots came back up I saw the dots were now just behind the arrows on both # 3 caps and both sprockets were off by a tooth though at first it looked like they were set properly. Moved the sprockets oriented one tooth so now the dots, arrows and TDC are in sync.

I oiled the cylinder walls (no oil in the engine at present) and rotated the engine by wrench to see if here were any obstacles to rotation and it turned easily enough but I could feel the friction from the newly honed walls.

Then I heard a clunk from the right side of the engine but didn't feel any restriction to rotation and I was going slowly so as to feel for anything like a valve hitting a piston, stopping rotation. I couldn't identify exactly where the noise came from and it wasn't at the same point in rotation. It almost sounds like it came from inside the case but I haven't opened the case. During the work I did I kept the holes covered and vacuumed the inside of the case with a vinyl tube attached to the vacuum cleaner to get out any particles of gasket or whatever that may have fallen in. The clunk is not reproducible in that I can't turn the engine over and hear the noise at the same time nor do I hear it on most revolutions.

I went ahead & checked the shims and came up with this:

Intake normal (.11~.15)
...gap....shim.....need shim
1 .20 ---285 --- 280
2 .12 ---275 --- 265
3 .13 ---290 --- 280
4 .19 ---290 --- 285

Exhaust normal (.21~.25)
...gap....shim.....need shim
1 .07 ---280 --- 275
2 .18 ---275 --- 280
3 .04 ---280 --- 270
4 .04 ---280 --- 270

Since the noise was not there at the moment I added a Tsb of oil to the cylinders and checked compression by using the starter and ran through 3-4 compression cycles each. When doing so I listened carefully for any clunk/noise and all sounded perfectly fine, just starter motor and the compressed gas coming out the spark plug holes/exhaust. Across all 4 cylinders though the compression was terrible, ranging from 60 to 80, nothing higher.

Because of that clunk and the low compression I have to wonder if somehow I bent valves before I got the chain properly in place and that caused the clunk I heard or is there something in the engine that with slow engine rotation would make noise when there is no oil in the engine? That it is irregular is curious.

If I did bend valves, how would I be able to tell this? All the buckets seem to be moving fluidly and I see no sign of binding.

Ideas?

[DGXSER]

Repeat yoru compression check but add a tsp of oil to each cylinder as you check it. If your numbers go up, then you know it is a matter of your rings needing to be reseated. If not, then it may be a valve issue. But before you go sweating a bent valve, did you lap the valves into the head when you had it off?

If you have not re-shimmed those valves, and those numbers are accurate, that could very well be the source of your bad compression numbers. With those exhaust valve readings, your valve is sitting open way to long. And incidentally, I would not change the shims on intake 2 and 3 myself. They are already in tolerance and not on the edge.

[KA1J]

No, I didn't lap them but I poured gasoline in each intake/exhaust port and nothing leaked into the valves. When I replaced the valve seals I looked carefully with a jewelers loop and all the valves looked as new on the mating surface; no sign of any pitting at all.

I'll go out & check the compression again.

I do need to find shims, I don't have any extra ones.

[WMarshy]

You could have bent a valve when your chain was off the sprocket... when I messed up replacing the CCT I turned the engine counter clockwise after I installed the new auto CCT and heard 2-3 clicks like the chain jumped. Tried to rotate it clockwise and had resistance so I concluded the valve was interfering with the piston. Had to take the cams out and set the engine to T and re-set the cams. Luckly I used a very light and and felt the resistance and didn't bend any valves...

What I would advise is doing kind of a leak down test. Really your interested in seeing if your valves are seating. Take an old spark plug and knock the ceramic out of it after cutting off the ground strap for the electrode. Once you have all the ceramic out of it you can tap it and screw in a fitting for your air hose. Have that piston at TDC so the valves are closed and apply air. Listen for air leaking from either the exhaust or intake boot. If they are seated well then you should only hear air leaking by the rings (put your ear to the oil fill hole). GL

PS. Make sure your valve clearances are correct first...

[KA1J]

Man, after all this mess I hope I didn't damage a valve/valves. I don't have an air compressor. The only one I know of is not movable & at a friend's place. I do have a mity-vac & have a tire compressor but it has one of the 90 degree heads and won't get in the head to fit on a fitting.

And I'm getting so much flack for having the bike under construction I'm going to have to relocate it somewhere soon.

Ugh...

[natemoen]

The low compression is most likely due to the new unseated rings. If you had a bend valve then you wouldnt be getting any compression in that cylinder/cylinders.

And put some oil in that engine before you start tuning it over with the starter again, those bearings need oil especially since it has been sitting empty for so long they are going to be BONE DRY!!!

[trdriver71]

Also do you have the carbs on? If so did you have the throttle open?

[KA1J]

Thanks for the replies.

I did form a leak down plug. Took a 14mm fitting that ended up in a schrader valve. I can't tell if there's any air coming out of the intake or exhaust ports, the air doesn't last long enough to show. I'm using a 12V tire compressor and it's noisy with little spurts of air, not a long continuous flow like from a tank so I really can't hear where the air is escaping from. I get 20-30 pounds of pressure showing on the gauge but nothing lasts more than a second & it's gone.

I haven't heard that clunk when wrenching the crank so if there's a bent valve or two it's pushed up out of the way of contact. The lifters seem to be moving in the correct manner but Gee, I have no idea what's normal. Even though the cylinders are honed, I thought with new rings the compression would be better than this in the beginning.

No carbs or exhaust is on at the moment so there's no restriction to air flow when doing the compression test.

[DAVINCI]

Didyou properly space the ring gaps so they're not lined up to each other?

[KA1J]

Heh, yes I did. I was following the service manual step by step and it has that drawing in there showing gap position. In fact, I had the engine back together & only then did I see in the rear section under Maintenance specifications that there was a bevel on #2 ring & it was then I was informed there was a top & bottom to the rings. I had to tear it down again to find 3 of the 4 #2 rings were upside down. Why in God's name if it was so important, didn't they put that drawing next to the ring gap orientation...

[TADracer]

YES! Get oil in that motor!

IMHO a compression check is nearly useless until you have the rings worn in. You will get a reading but it will not be a true reading. Besides, a compression check must be done at operating temp and with throttle wide open and you cannot do the first thing with an unstarted motor. A leakdown test will not give a true reading either until everything is worn in but, it will at least still identify a leaking/bent valve right off the bat. The 'klunk' you heard turning it over by hand might just be nothing more than the starter motor clutch releasing itself, especially if it has been sitting for awhile. These motors can make all kinds of goofy noises until they get everything rotating in the same direction again after a re-build.

Call me a gambler but I would adjust those valves, make sure everything else is in good initial adjustment, turn it over by hand clockwise a few times with valve cover off to make sure everything seems smooth upstairs. Then valve cover on and use the starter with spark plugs out until you get some oil pressure. If everything seems OK, then plugs in and start her up.

[tcoop]

I'm not sure I understand the valve clearence so I would like to have some clarification on the shims needed...


Intake normal (.11~.15)
...gap....shim.....need shim ---- My guess
1 .20 ---285 --- 280 ------------- 290? To make Gap smaller
2 .12 ---275 --- 265 ------------- Already in spec
3 .13 ---290 --- 280 ------------- Already in spec
4 .19 ---290 --- 285 ------------- 295? To make Gap smaller

Exhaust normal (.21~.25)
...gap....shim.....need shim
1 .07 ---280 --- 275 ------------- 265?
2 .18 ---275 --- 280 ------------- 270?
3 .04 ---280 --- 270 ------------- 260?
4 .04 ---280 --- 270 ------------- 260?


When I put my 80 Special back to geather I want to make sure I do it right.
Is there a chart to go by?

The first TWO time I put the head back on my 78... I bent the valves, so I am no expert when it come to working on these bikes but I am trying to learn.

[bikerphil]

Valve shim charts are in post #11...

http://www.xs11.com/forum/showthread...lve+shim+chart

[KA1J]

So today I reshimmed the engine and the compression results are:

Cyl 1: 90 dry - 100 after adding oil to the chamber

Cyl 1: 88 dry - 90 after adding oil to the chamber

Cyl 1: 93 dry - 115 after adding oil to the chamber

Cyl 1: 90 dry - 115 after adding oil to the chamber

This is with honed cylinders and new rings.

As I mentioned in the initial post I heard a few clunks coming from the right side of the engine /crankcase while having issues getting the cam chain to play nice with the crank and cams. I was wrenching the crank, not using the starter; the engine was drained of oil and the clunks went away quickly after 5-6 rotations of the crank while I assured the dots and TDC were finally in sync. With just turning the engine over by starter there is no mechanical noise other than the starter motor.

I honestly have no idea but if I bent the valves while having the cam chain off to the side of the sprockets & while trying to check if the cam dots/arrows & TDC were sustained through a revolution (at first they were not and both the intake & exhaust were off one tooth on the cam chain)... Would I see the kinds of compression I'm seeing now; that these low numbers could be caused by a bent set of valves?

Or are these readings normal, and they show there is no valve damage and I should expect to see a nice jump in compression after the rings seat?

I really am going at this unknowing what to think or expect...

Ugh...

[bikerphil]

If you had a bent valve, your compression on that cylinder would be zero. Looks like you got lucky.